Fractionation method for nucleotide fragments

Abstract: A fractionation method for DNA fragments according to the present invention comprises a first step of preparing a probe chip or a set of probe chips immobilizing independently a DNA probe having a first sequence part having a specific known sequence part together with a part of enzyme recognition sequence and a second sequence part composed of a combination of one to six bases adjacent to the first sequence part at 3' terminus, a second step of introducing a DNA oligomer composed of a part of enzyme recognition sequence and a sequence complementary to the known sequence part into the fragment termini of DNA fragments from restriction enzyme cleavage, and a third step of placing the probe chip or the set of probe chips in a solution containing the nucleotide fragments with the introduced DNA oligomer produced at the second step, for at least hybridization and the complementary strand extension of the DNA probe, whereby the DNA fragments are fractionated.

Description: BACKGROUND OF THE INVENTION The present invention relates to a fractionation method for nucleotide fragments (DNA or RNA) and a DNA sequencing method of the same. When DNAs of different lengths are in the state of a mixture, for example, in the state of enzyme cleaved products of a long DNA, it is impossible to immediately determine their DNA sequences. Conventionally, two methods are known as the method for analyzing such DNA sequences. A first method comprises separating individual DNA fragments by gel electrophoresis and subjecting the separated individual fragments to DNA sequencing. A second method comprises inserting these DNAs into an appropriate vector (cloning), injecting the vector into E. coli which is then cultured on agar medium, reculturing E. coli in each generated colony and extracting DNA from the bacterium in multiplication for DNA sequencing. SUMMARY OF THE INVENTION For gel electrophoresis to be used for DNA separation, agarose gel or polyacrylamide gel may be used. By gel electrophoresis, the difference of a single base in DNA of a length of 400 b or less may be discriminated, and furthermore, DNA of a length of 300 b or less may be separated and fractionated. However, as the length gets longer, the separation potency of the gel may be lowered. Therefore, the first conventional method is problematic because individual DNA fragments cannot always be separated with identical fractionation results. Alternatively, the second conventional method via cloning is also problematic because the method demands laborious works; because a DNA fragment of a far shorter length cannot be cloned; and because a vast number of clones may be required for DNA sequencing if all clones corresponding to all fragments should be separated, so as to secure the analysis of all fragments. A DNA fractionation method utilizing hybridization is known, comprising immobilizing DNA probes of various DNA sequences onto a solid surface and hybridizing objective DNA fragments with the probes, whereby the fragments are separated and fractionated. However, it is necessary in this case that the sequences of the objective DNA fragments should be known to prepare the probes on a solid surface, so the method is not applicable to DNA fragments with unknown sequences. The present invention overcomes these problems, and is to provide a method for readily separating DNA fragments, an analytical method of DNA sequence and the like. The present invention relates to a fractionation method for DNA fragments, comprising treating a mixture of DNA fragments having a terminus bonded with an oligonucleotide of a known sequence with a probe chip or a set of probe chips which have a solid surface on which various DNA probes are immobilized, said DNA probes having a sequence selecting part of an oligonucleotide of a length at which length the oligonucleotide cannot hybridize solely in a stable fashion, i.e. an oligonucleotide of one to six bases, at the 3' terminus adjacent to the specific known oligonucleotide sequence complementary to the terminus part of the above DNA fragments, and fractionating the mixed DNA fragments, at least through the process of hybridization and complementary DNA strand extension reaction. Stable hybridization is incurred in the specific DNA sequence, while the sequence selecting part is used for screening the occurrence of the DNA complementary strand extension. When the DNA complementary strand extension occurs to an oligonucleotide probe being hybridized with a DNA fragment perfectly, the hybridization force increases which can be used to separate the DNA fragment from other DNA fragments hybridized to oligonucleotide probes inperfectly; therefore, the DNA strand extension does not occur. By the fractionation method described above, fractionated DNA fragments can be separated and collected, if necessary. Such probe chip includes, for example, a slender rod, wire, a strip of sheet, ribbon, etc., on which DNA probes are immobilized, or a solid surface with sections on which different types of DNA probes are individually immobilized. By the method, a single probe chip or a plurality of probe chips retaining DNA probes, are simultaneously placed in a solution containing DNA fragments, for DNA complementary strand extension reaction to generate double stranded DNA(s), which is (are) then fractionated individually or collectively with plural types. According to the method, at least one repetition is made of a cycle of the process of DNA complementary strand extension reaction and a process comprising raising the temperature of a mixture of resulting the complementary strand extension reaction products to separate the non-extended DNA probe from the DNA fragment sample, while leaving the extended DNA probe hybridized to the DNA sample. In the above method, when DNA complementary strand extension reaction is carried out, using probe chips where DNA probes are individually immobilized onto different solid surfaces or are individually immobilized onto different sections of a solid surface, together with a free oligonucleotide oligomer (primer), the number of DNA fragments can be amplified and separated on the solid surface by raising and then lowering the reaction temperature repeatedly , which is a kind of PCR (Polymerase Chain Reaction) with a solid surface. Here, the DNA probe immobilized onto the solid surface contains a common sequence and a sequence selecting part at 3' terminus, although the free primer contains only a common sequence. The DNA fragments obtained by the fractionation method in accordance with the present invention are used for DNA sequencing, as they are or after individual separation and isolation. The DNA sequencing method in accordance with the present invention can be applied to DNA sequencing of DNA fragments after fractionation as described above or of DNA fragments after separation or isolation without individual fractionation. By attaching a known DNA oligomer to the terminus of a DNA fragment, the DNA fragment is modified into a form hybridizable to a DNA probe. A sequence selecting part of several bases attached to the 3' terminus of the DNA probe is arranged so as to select an objective DNA fragment, and therefore, the DNA probe is a probe for selection. For the sequence of several bases at 3' terminus, all combinations of several bases should be prepared. DNA probes each having a sequence selecting part composed of a sequence from such combination and a known sequence complementary to a specific DNA fragment are attached individually to the tips of different slender rods. When the sequence adjacent to the 3' terminus of one of these DNA probes is completely matched, DNA complementary strand extension proceeds with the resultant stability increase for hybridization, so that mismatched sequences around the terminus can be discriminated from such sequence by raising the temperature. As the sequence of the probe, adjacent to the several bases at 3' terminus for selecting DNA fragment, is common to all probes attached to slender rods, all DNA fragments hybridize to DNA probes. However, a great number of so-called mismatched pairs (a pair of DNA fragment and DNA probe), which are not attached to each other at 3' terminus, are present at a stage where DNA fragments and DNA probes are mixed to form hybridomers. The DNA complementary strand extension occurs only for the completely matched pairs. Thus, a DNA fragment hybridized to a probe without complementary strand extension is dehybridized and then rehybridized to another probe, while a DNA fragment hybridized to a probe extended by complementary strand extension reaction is left as it is. By repeating such procedure, the number of a pair (i.e. a pair of a DNA fragment and the DNA probe) having a sequence matched with the sequence around the 3' terminus of the DNA probe and suffered with DNA complementary strand extension can be increased. In such manner, pairs in complete hybridization are separated. In accordance with the present invention, DNA fragments of unknown DNA sequences can be separated on the basis of the difference in their terminal sequences. The separated DNA fragments are fractionated and amplified by PCR for sequencing. Thus, DNA analysis can be done without conventional cloning process requiring much labor and a longer time. Also, the present invention is applicable in various fields, because any DNA libraries can be separated and isolated on the basis of their terminal sequences. The present invention can be summarized as follows. Preparing a probe chip or probe chips immobilizing each DNA probe individually on a solid surface, the sequence of which has a specific known sequence part, a part of restriction enzyme recognition sequence, (the combined sequence is a first sequence part) and a sequence selecting part of 1 - 6 bases at 3' terminus (a second sequence part) adjacent to the known sequence part, introducing the known sequence part into the fragment termini of a DNA fragment mixture from restriction enzyme cleavage, contacting the probe or probes to the mixture DNA fragments for hybridization with the DNA fragment mixture, thereby extending complementary strands, individual DNA fragments are separated by the difference of hybridization stability. The DNA fragments are used for sequencing as they are or after isolation and amplification. DNA fragments with unknown DNA sequences can be separated on the basis of the difference in sequence around termini, whereby cloning process can be shortened dramatically. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of the DNA extraction in accordance with the present invention; Fig. 2 is a schematic view of the DNA extracting slender rods in a bundle in accordance with the present invention; Fig. 3 is a view depicting the method for analyzing two bases at DNA fragment terminus; Fig. 4 is a schematic view of the detector for the analysis of the two bases at DNA fragment terminus; Fig. 5 is a view depicting another method for analyzing two bases at DNA fragment terminus; and Figs. 6A to 6E are views depicting one example of DNA sequencing results using the method of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be explained in examples. The technical scope of the present invention is not limited to these examples, however. With reference to Figs. 1 and 2, the principle of the present invention will be explained in a simple example. Through ligation, firstly, DNA oligomer 2 having a known sequence is ligated to the terminus of double stranded DNA fragment 1 produced by restriction enzyme cleavage. Here, the part of ligated oligomer and the recognition sequence of enzyme is the known sequence part. Otherwise, poly A is attached to the terminus of single stranded DNA with terminal transferase, to introduce the known sequence into the terminus. In Fig. 1, explanation will now be made, by illustrating an example of sample fragment 3 with known sequence oligomer 2 introduced into the terminus of the double stranded DNA fragment 1. DNA probe 12 is attached to the tip of slender tube or slender rod 11. The DNA probe 12 attached to the slender tube or slender rod 11 is composed of sequence selecting part 14 of several bases at 3' terminus and known sequence part 13. Herein, DNA probes 12 each having the sequence selecting part 14 having a different sequence from each other are individually attached to slender tube or slender rods 11, and in the example shown in Fig. 1, the sequence selecting part 14 is composed of two bases while the known sequence part 13 is composed of fifteen bases (one circle does not represent one base). The base length of the known sequence and the selective sequence is long enough to make stable hybridization with DNA fragments. The slender rod 11 is immersed in a sample solution containing sample fragment 3 and then the sample fragment 3 is denatured followed by annealing. The resulting objective DNA fragments 41, 42 are hybridized with the DNA probe 12 for DNA complementary strand extension. During this reaction, hybridized DNA probe 12 without mismatch at their 3' terminus may generate DNAs 51, 52 through complementary strand extension; otherwise, complementary strand extension may not proceed for DNA probes with mismatch at their terminus because mismatched DNA fragment 41 may generate hybridized DNA fragment 61. So as to dehybridize the mismatched DNA fragment 61 from the probe, the temperature of the sample solution is raised to 70 to 85°C. Subsequently, the temperature is lowered to hybridize the objective DNA fragments 41, 42 with the DNA probe for complementary strand extension. After repeating such procedure, the solution is kept at a higher temperature and the slender rod 11 is drawn out at a higher temperature to collect the fragments hybridized with the extended probes, while leaving the mismatched DNA fragment in the solution. Then, the tip of each slender rod is transferred into a different bottle filled with a buffer solution, then the temperature of the rod is raised to dehybridize the DNA fragment from the probe on the tip. By bundling a plurality of slender rods (A, B, C, ----) of Fig. 1 as shown in Fig. 2 to make a set of slender rods 101 (A, B, C, -----, I, J), the reaction process described above may progress simultaneously. Each slender rod tip is immersed in a buffer solution, and by raising the temperature, DNA fragments each having a matched 3' terminal DNA sequence with the DNA probe immobilized on the slender rod are fractionated. Using the fractionated DNA fragments, DNA sequence is determined. (Example 1) Hind III digestion products of λ-phage DNA were used as samples. Fragments from restriction enzyme cleavage are ligated to a fluorescence (sulforhodamine 101) labeled DNA oligomer via ligation reaction. Alternatively, a surface of a glass rod (a 0.2-mm diameter at the tip) is treated at a length from the tip to 5 mm below for attaching DNA probes having an amino residue at 5' terminus, thereby preparing a large number of glass rods each immobilized with the DNA probe at the tip thereof. For immobilization, silanization reaction is used to introduce various activated residues onto the glass surface. For example, the glass surface is treated with dilute aqueous acetic acid solution of 3-glycidoxypropyltrimethoxysilane, and is then baked at 90 to 105°C to introduce the epoxy group onto the glass surface. Then, reaction with a 5'-amino DNA probe at pH 9 generates a glass rod retaining the DNA probe on the glass surface thereof. Another method comprises introducing an amino residue onto the glass surface using 3-aminopropyltrimethoxysilane, 3-(2-aminoethylaminopropyl)trimethoxysilane, etc., and treating the surface with succinic anhydride, thereby introducing the carboxyl group into the amino residue. Subsequently, reaction with a 5'-amino DNA probe in the presence of water-soluble carbodiimide generates a glass rod retaining the DNA probe. The DNA sequence of the DNA probe is composed of at least a common sequence part, which is a complementary sequence (which is the same as the sequence at 5' terminus) to the sequence at 3' terminus of the fluorescence labeled oligomer used for the ligation to the DNA fragments, a part of enzyme recognition sequence, and a sequence selecting part of an appropriate sequence of two bases at 3' terminus. The selectivity reaches highest when the terminal sequence selecting part is composed of one to two bases. The number of a combination of terminal two bases is 16, so 16 types of slender rods individually retaining 16 DNA probes are to be prepared. The 3'-terminal sequence selecting part may be composed of three to four bases, and in the case of three bases, 64 types of such slender rods should be prepared. For four bases, 256 types of such rods should be prepared. When the length of a terminal sequence selecting part is longer, complementary strand extension may sometimes occur even if the base matching between probe DNA and sample DNA is insufficient. So as to prevent such extension occurred for mismatched pairs, terminal hybridization potential should be distinctively decreased to prevent a stable hybridomer formation among mismatched pairs at a terminal. When several bases in the common sequence part and especially bases adjacent to a sequence selecting part at 3' terminus is modified into inosine or is modified into a mismatched sequence, the stability of hybridization around the terminus then depends largely on the matching of the sequence selecting part, and thus, can be adjusted so that the complementary strand extension does not sufficiently proceed if even a single base is mismatched in the sequence selecting part. The length of the sequence selecting part may preferably be 6-mer or less which singly does not form a stable hybridized product, and is more preferably 1-mer to 3-mer because complementary strand extension is much affected by the degree of base matching at 3' terminus of 1-mer to 3-mer. Then, a part of fluorescence labeled fragments produced by ligation is fractionated and analyzed by gel electrophoresis to generate a gel electrophoresis pattern of the fragments. When the number of the fragments appearing the electrophoresis patterns is more than ten in a single stranded form, the DNA species in a fraction is too more to analyze without separation. Therefore, DNA fragments are separated and fractionated again via gel electrophoresis. Finally, the number of fragments contained in a fraction should be 10 or less in a single strand form. This is because the number of DNA probe types to be used subsequently for DNA separation should be 16, so that the trapping of more than two DNA fragment species by a single probe species should be prevented. In the case of Hind III digestion product of λ phage, the number of fragments is 14, but the fragments were used for sequencing without separation as a trial. Dissolving the DNA fragments in a buffer solution, 16 slender rods each immobilized with individual 16 types of DNA probes are immersed in the solution for hybridization. So as to promote hybridization, double stranded DNA may be thermally denatured or its 3' terminus may be modified into a single stranded form by exonuclease digestion at the 5' terminus of the double strand. Deoxynucleotide triphosphate (dNTP) as substrates for complementary strand extension are added together with DNA polymerase, to promote complementary strand extension. Because complementary strand extension proceeds for DNA probe with 3' terminus in completely matched hybridization with a DNA fragment, the bonding strength of the DNA probe to the DNA fragment is increased. On the other hand, complementary strand extension does not occur on a DNA probe under a partially mismatched hybridization condition so such bonding strength is weak. From a statistical reason, only 1/16 of DNA fragments can hybridize to the probe without mismatch by the hybridization procedure comprising once immersing 16 slender rods in the solution and simultaneously immersing 16 types of DNA probe chips in a solution containing DNA fragments. After complementary strand extension terminates, thermal denaturation by elevating temperature up to 70 to 80°C is carried out to promote dehybridization of DNA fragments from a probe. Then, the temperature is lowered to hybridize DNA fragments again to non-extended another probe for complementary strand extension. By repeating such procedure, the number of a DNA pair in complete matching can be increased. If repeating the cycle at a number larger than the number of the DNA probe types, an objective DNA fragment can be trapped almost completely with a matched DNA probe, which is then isolated. A smaller number of the DNA probe types to be simultaneously hybridized decreases the number of repetition of such procedure required for sufficient isolation. Thus, practical means is illustrated, such as the use of a single DNA probe chip, the use of a set of four to five probe chips, the use of DNA probe chip having only necessary 2-base sequence adjacent to the common sequence part of DNA fragments, and the like. So as to identify the 2-base sequence adjacent to the common sequence part of DNA fragments, use is made of glass rod 11 immobilized with a DNA probe having A, C, G and T as the first base adjacent to the common sequence part, following the procedure shown in Fig. 3. Bundle 110 of 16 slender rods, each group of four rods having a set of A, C, G and T termini, is reacted for hybridization simultaneously with a sample mixture solution. After the hybridization reaction, the glass rods are washed in water to wash off the non-hybridized sample, and then, the bundle 110 is divided into four probe groups, each probe group having a set of A, C, G and T termini. As shown in Fig. 3, consequently, hybridized DNA 111 is captured onto the glass rods. Subsequently, by adding fluorescence labeled terminator 112 (dideoxynucleotide triphosphate; ddNTP*), ddNTP* is introduced as a second nucleotide adjacent to the common sequence part of the DNA probe, by DNA polymerase reaction (Symbol "*" represents fluorescence label). By the method shown in Fig. 4, the sequence information up to the second base adjacent to the common sequence part of required DNA probes is brought about by measuring the presence or absence of the fluorescence on the surface of the glass rods. The method shown in Fig. 4 comprises expanding the laser beam from laser source 121 through beam expander 122, collimating the laser beam via lens 124 and introducing the laser beam through photocoupler 127. The laser beam projected onto the glass rod 11 reaches the top portion of the glass. Fluorescence is emitted if a fluorphor bonds to the DNA probe on the glass surface through the above reaction. Fluorescence progresses sequentially through the glass rod 11 and the photocoupler 127. Then, its direction is changed via dichroic mirror 123. The beam passing through filter 125 is introduced through the lens 124 into photodetector 126. By detecting the fluorescence from each glass rod and analyzing the data of detected signals with a computer, the terminal base sequence and a fluorescence emitting terminator can be identified. In other words, the terminal sequence of DNA fragments up to the second base can be identified by checking the type of a first base adjacent to the common sequence part and the type of the fluorescence labeled terminator introduced into the second base. If fluorophors of different wave lengths are used for four types of fluorescence labeled terminators, i.e. dideoxyadenosine triphosphate ddATP*, dideoxycystein triphosphate ddCTP*, dideoxyguanosine triphosphate ddGTP* and dideoxytimine triphosphate ddTTP*, the reaction of a set of 4 slender rods instead of 4 rods will be sufficient. In such a case, the type of bases up to the second base adjacent to the common sequence part can be identified on the basis of the difference in fluorescence wave length. For another method to identify the 2-base sequence adjacent to the common sequence part of DNA fragments, DNA probes which have A, C, G and T as the bases adjacent to the common sequence part are prepared. The length of each DNA probe should be modified such as those of the DNA probes 200, 201, 202, and 203 as shown in Fig. 5, so that they can be identified individually by size separation by electrophoresis. After preparing a solution containing both sample DNA 204 and the aforementioned primers 200, 201, 202 and 203 for complementary strand extension, the solution is divided into four parts to check a second base species. To the individual divided solutions are added fluorescence labeled terminator 112 and DNA polymerase reactions are carried out. In such manner, fluorescence labeled terminator 205 bonds to the part of the second base adjacent to the common sequence part of the DNA probe. The reaction products are analyzed by electrophoresis for determining the terminal base species of the reaction products. From the electropherogram, the sequence information up to the second base adjacent to the common sequence part can be obtained. With an electrophoretic device for use in the electrophoretic analysis as shown in Fig. 5, laser beam 210 from laser source 206 irradiates electrophoretic gel 209 from the direction almost perpendicular to the direction of DNA fragment migration, to detect DNA band of probe 220 with an introduced fluorescence labeled terminator. The fluorescence from DNA bands is detected with photodetector 207. So as to simplify the explanation of principle, Figs. 3 to 5 illustrate a case where the sample DNA is single strand. As demonstrated in the present example, however, the information up to the second base adjacent to the common sequence part can be obtained even for a mixture containing a plurality of DNAs. In this example, it was found that eight types of probes were in complete matching with DNA fragments. Another example is illustrated wherein by using a slender rod (probe chip) immobilized with DNA probes, DNA fragments produced by Hind III digestion of λ phage DNA were separated for DNA sequencing. Fourteen types of DNA fragments were produced by digesting λ phage DNA with Hind III. As shown in Fig. 3-3, oligomer 2 of a known sequence is introduced into the terminus of the produced DNA fragments. As shown in Fig. 1, DNA probe 12, composed of known sequence part 13, which is complementary to the oligomer introduced into the DNA fragment terminus and a part of Hind III recognition sequence, and a sequence selecting part 14 having appropriate two bases adjacent to the 3' terminus of the known sequence part 13, is immobilized onto the separating rod. Because the number of combinations of appropriate two bases at the sequence selecting part amounts to 16, 16 types of DNA probes are necessary for separation DNA fragments. Thus, the number of slender rod types amounts to 16. According to the mentioned immobilization method, slender rods immobilized with the DNA probe are produced. In a solution containing 14 types of DNA fragments introduced with the oligomer of a known sequence is immersed a bundle of probe chips, produced by bundling individual slender rods immobilized with the 16 types of DNA fragments as prepared as described above. After thermal denaturing DNA fragments in the solution the DNA probes immobilized onto the slender rods react with the DNA fragments under hybridization conditions. Continuously, complementary strand extension progresses on the completely matched pairs. Furthermore, 30 cycles of such denaturing and hybridization followed by complementary strand extension are repeated. DNA fragments with 3' termini in incomplete hybridization as well as unreactive substances on the slender rods are washed off in aqueous solution at 70 to 80°C. By the method described above, DNA fragments in complete hybridization can be fractionated. By using a device as shown in Fig. 4, the slender rods on which the DNA fragments are in complete hybridization can be isolated. By heating to 96°C the slender rods with the hybridized DNA fragments, the hybridized DNA fragments are released from the rods and fractionated. The sequences of the fractionated DNA fragments are determined by dideoxy terminator method using a fluorescence labeled primer. For example, Fig. 6 shows a part of the sequencing results of the DNA fragments isolated from the slender rods immobilizing a DNA probe where a sequence selecting part at 3' terminus is GC. For sequencing by the dideoxy terminator method, use is made as the primer of a DNA oligomer where a sequence selecting part at 3' terminus is GC as is the DNA probe immobilized on the slender rod. The sequencing reaction products by using four types of terminators (ddATP, ddCTP, ddGTP and ddTTP) are distinguished by different electrophoretic migration tracks for fluorescence detection. It is shown in Figs. 6A, 6B, 6C and 6D, electropherogram of the sequencing reaction products produced by using the four types of terminators, ddATP, ddCTP, ddGTP and ddTTP. These electropherogram sets are shown simultaneously in Fig. 6E. In Figs. 6A to 6D, the DNA bands corresponding to different bases are observed at different migration periods; the peak position does not overlap which indicates there is only one DNA fragment species to be analyzed in the sample solution. If the isolation of DNA fragments from a mixture is insufficient and there are plural of DNA fragments in a sample, a plurality of peaks (four peaks derived from A, C, G and T, at maximum) should be observed at the same peak positions. No overlapping of peak positions as shown in Figs. 6A to 6D verifies that the isolation and fractionation of DNA fragments according to the present invention is satisfactory. The base species, therefore the sequence, are as shown in the figures. As has been described above, the sequence is obtained as shown in sequence No. 1, which corresponds to a partial sequence of λ phage DNA. As demonstrated here, the fractionation method in accordance with the present invention is advantageous in sequencing a plurality of DNA fragments directly from the mixed state thereof without cloning procedure. In the above example, DNA fragments trapped on probe chips are used for analysis, but DNA probes extended on solid surface may be used for analysis as well. When a complementary strand extends in full length by using a DNA probe immobilized on the tip of a slender rod as a primer for complementary strand extension, the common sequence part should appear at 3' terminus of the extended probe (the oligomer bonds to both ends of a double strand DNA fragment through ligation), so that the analysis can be started from the 3' terminus of the extended strand by using a primer of a known sequence. Also, when a trapped DNA strand is long, the DNA is separated, prior to the cleavage with another restriction enzyme to digest the DNA into smaller fragments, which are then repeatedly subjected to the above procedure. In the above example, the probability of extending complementary strand is increased by repeating hybridization followed by DNA strand extension and dehybridization of DNA probes to DNA fragments. When a free primer having the common sequence part is added to the solution, PCR (polymerase chain reaction) progress simultaneously to increase the DNA fragment copy number during separation. For the objective of such application, it is preferable from the respect of efficiency that the common sequence parts bonded to both termini of DNA fragments should be different from each other, so that an immobilized probe and a free primer have individually different common sequence parts, each part thereof being of a different sequence. PCR amplification using DNA probes immobilized separately according to their sequences on a solid support along with a free primer, provides a novel means for separation and amplification of a mixture. The DNA hybridized to an immobilized probe of which a complementary strand is extended resides substantially around the fraction immobilizing the probe which extended to produce complementary strand at a higher temperature of about 95°C which temperature is for thermally dissociating a double strand into single strands. Alternatively, the DNA and DNA probe pair without complementary strand extension is less stable and it is readily dehybridized into single strands during the process of temperature elevation. This pair forms double strand more slowly during the process of temperature decrease. Therefore, the probability for the DNA to hybridize to another DNA probe becomes large after the single stranded DNA diffuses into another fraction remote from the position where first hybridization occurs, and while repeating the process, the probability of the DNA reaching to DNA probe for stable hybridization is raised. Alternatively, when the single stranded DNA forms a double strand with a completely hybridizable DNA probe, complementary strand extension is initiated for increasing the stability; during the process of temperature increase, the dissociation of double strand occurs more lately, while during the process of temperature decrease, more speedy hybridization occurs. Therefore, large migration of DNA by diffusion does not occur. By presetting the annealing temperature as the lower temperature at a higher temperature, such phenomenon can be more readily promoted. By repeating such procedure, screening and multiplication of DNA strand into individual fractions can be done. In the above example, various DNA probes are used after immobilization onto solid surface such as slender rods individually separable, but the material is not limited to glass rods herein used. Also, the surface of plate materials such as glass plate may be fractionated to immobilize individual DNA probes for fractionation. Example 2 Example 2 is an example to use the fractionated DNA fragments as template of DNA sequencing. As in Example 1, DNA fragments are grouped and retained on the top of strips of ribbon for extending complementary strand. At the 3' terminus of the extended complementary strand is located the same common sequence as that of the oligomer previously attached via ligation. By raising temperature, the double strand is thermally dissociated into single strands, and then, all the strips are transferred into a vessel containing a reaction solution for DNA sequencing. As a primer, a complementary sequence to the common sequence at the 3' terminus is used. It is convenient to use the terminator ddNTP (dideoxy nucleotide triphosphate) labeled with different fluorophors depending on the base type. When a fluorescence labeled primer is used, four DNA extended strands immobilized on the strips of ribbon should be prepared to synthesize a fragment family with different base types for sequencing. After the termination of sequencing reaction, fragments of various lengths synthesized by using DNA polymerase reaction with a common primer are retained on the 3' terminus of the extended DNA of which the 5' terminus is immobilized on the top of the ribbon. Placing the strips of ribbon onto the upper top of a gel plate, heating the ribbon for releasing the fragments produced by sequencing reaction for gel electrophoresis to identify the fragment length, the sequence is determined. The strips of ribbon are placed at different positions depending on the probe type, and the DNA fragments dissociated therefrom are separated by electrophoresis.

Claims: A fractionation method for DNA fragments comprising the steps of: i) preparing a probe chip or a set of probe chips independently immobilizing a DNA probe; ii) ligating an oligomer having a known sequence to the 3' terminus of digested DNA fragments formed by restriction enzyme digestion; iii) placing the probe chip or the set of probe chips in a solution containing the digested DNA fragments ligated to the oligomer produced in step ii) for hybridizing the digested DNA fragments ligated to the oligomer to the DNA probe and extending the resulting hybridized DNA probe by complementary strand extension reaction in the solution; and iv) raising the temperature of the solution resulting from the complementary strand extension reaction in step iii) and removing the DNA fragments hybridized with the DNA probe not extended by the complementary strand extension reaction, while leaving the extended DNA probe hybridized to the digested DNA fragments ligated to the oligomer; wherein the DNA probe has a common sequence part and a sequence selecting part adjacent to the common sequence part at the 3' terminus, the common sequence part is complementary to the sequence of the oligomer ligated to the 3' terminus of the digested DNA fragments and an enzyme recognition sequence part, and the sequence selecting part is composed of one to six bases and is any possible combination of the one to six bases; and wherein step iii) and step iv) are repeated at least once, whereby the DNA fragments are separated or fractionated. The fractionation method for DNA fragments according to claim 1, wherein the probe chip is any one of a slender rod, wire, sheet, and ribbon. The fractionation method for DNA fragments according to claim 1 or claim 2, wherein the probe chip has a plurality of sections on a solid surface and each combination of the one to six bases in the sequence selecting part of the DNA probes is immobilized onto each section. The fractionation method for DNA fragments according to any of the claims 1 to 3, wherein the probe chip(s) is/are simultaneously placed in the solution containing the DNA fragments and the generated double stranded DNAs are fractionated by each single type or collectively by a plurality of the types. The fractionation method for DNA fragments according to any of the claims 1 to 4, wherein the probe chip has a plurality of sections on a solid surface and each combination of the one to six bases in the sequence selecting part of the DNA probes is immobilized onto each section or the individual DNA probes are immobilized onto different solid surfaces and wherein a free oligomer is used for the complementary strand extension reaction in step iii), and the complementary strand extension reaction is progressed by raising or lowering the temperature, whereby DNA is selected. The fractionation method for DNA fragments according to claim 5, wherein the probe chip has a plurality of sections on a solid surface and each combination of the one to six bases in the sequence selecting part of the DNA probes is immobilized onto each section and the common sequence part is common to the DNA probes. The fractionation method for DNA fragments according to any of the claims 1 to 4, wherein a free oligomer having a sequence identical to the common sequence part is added to the solution in step iii), and a polymerase chain reaction progresses simultaneously to increase the number of copies of the digested DNA fragments ligated to the oligomer by raising and lowering the temperature of the solution to effect the polymerase chain reaction. The fractionation method for DNA fragments according to any of the claims 1 to 7, wherein the oligomer is labelled with a fluorophore. The fractionation method for DNA fragments according to any of the claims 1 to 8, which comprises the additional step of determining the DNA sequences of the DNA fragments generated according to any of the claims 1 to 8 as they are or after separation and isolation.

Inventors: KAMBARA HIDEKI, OKANO KAZUNORI, UEMATSU CHIHIRO, KAMBARA, HIDEKI, OKANO, KAZUNORI, UEMATSU, CHIHIRO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1994
Main classification: C07H1
IPC codes: G01N33, C12Q1, G01N27, G01N37, C12N15